In recent years, a communication service capable of processing a lot of data including a motion picture, etc. for a smart phone, etc. becomes available. To this end, it needs to significantly increase a communication capacity in a conventional technology field. There is a DWDM (Dense Wavelength Division Multiplexing) which is able to increase a communication data using a previously installed optical fiber. The DWDM is directed to a method wherein lights with different wavelengths can be simultaneously transmitted using one optical fiber, which operation is available because there is not any interference between signals even though light signals of various wavelengths are transmitted at the same time through one optical fiber based on a principle wherein different laser lights with different wavelengths don't interfere with each other.
Now, a standard called NG-PON2 (Next Generation-Passive Optical Network Version 2) is being agreed throughout the world. The NG-PON2 standard uses a wavelength-tunable laser which is able to accommodate a 4-channel of 100 GHz frequency interval as a standard of an optical communication module installed at the side of a subscriber. The optical module for a subscriber of the NG-PON2 uses as basic standard a transceiver module called SFP (Small Firm Factor Pluggable). Here, since the SFP module package has a small volume, a 4-channel wavelength-tunable laser module should be made compact-sized.
Now, a wavelength-tunable laser of various types is being developed and sells in the market, however it in almost cases is made in a butterfly packet type with a photoelectric element which is large in volume, whereupon a large volume photoelectric element cannot be accommodated in a SFP transcriber module. The photoelectric element package sized to be accommodated in the SFP transceiver is a TO (Transistor Outline) type package, but a wavelength tunable TO type photoelectric element wherein a wavelength is tunable in a TO type is not yet available.